There are several different cuts of Futura out there from different foundries (Linotype, Bitstream, URW, ParaType, Tilde, Neufville, Elsner+Flake, Scangraphic, etc). Then there's variants of Futura, like Futura Maxi from Monotype or Futura Next from Neufville Digital. None of these cuts are identical or interchangeable. There's lots of subtle differences. Those differences can be a real PITA if you're having to do something like replace a cracked channel letter face and you don't have the original art files to create a replacement face. If it doesn't line up with the versions of Futura you have in your own font collection you'll be stuck having to create a pattern as best as you can from the cracked face and manually saw or rout out a replacement.
Let's not forget the truly aggravating, amateur-hour, hack, vomit problem of countless numbers of sign people squeezing and stretching fonts when they have no business doing that awful looking garbage. Aside from the hack amateur look of things that comes about from distorting fonts it creates all sorts of work flow problems for service work. When some idiot manually squeezes or stretches the letters on something like a channel letter sign design it really won't matter if you have the exact same typeface in your own collection. You have to guess the exact level of squeeze or stretch that was doofus-applied to the letter forms. In the end it's just faster making a pattern of the damaged letter and creating a replacement that way.
Custom designed lettering and glyphs, even something like an altered Futura apostrophe, will pose similar problems for replacement graphics or letter faces. You need the original art files for an exact match. I won't fault someone for creating a custom lettered sign from scratch, especially from his own hand lettering or hand digitized files. That's a good thing. But I can't do anything but have complete disdain and even hatred for this awful habit of squeezing and stretching fonts. And when a sign guy is squeezing and stretching Arial I'm thinking that hack just needs to go do a different job for a living. He's literally dropping his drawers and taking a dump on the graphic design profession when he does that nasty garbage.